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Re: [Qemu-devel] Windows balloon driver PFN issue
From: |
Peter Xu |
Subject: |
Re: [Qemu-devel] Windows balloon driver PFN issue |
Date: |
Thu, 1 Feb 2018 10:33:50 +0800 |
User-agent: |
Mutt/1.9.1 (2017-09-22) |
On Thu, Feb 01, 2018 at 04:24:40AM +0200, Michael S. Tsirkin wrote:
> On Thu, Feb 01, 2018 at 10:18:53AM +0800, Peter Xu wrote:
> > On Wed, Jan 31, 2018 at 04:03:12PM +0200, Michael S. Tsirkin wrote:
> > > On Wed, Jan 31, 2018 at 05:28:35PM +0800, Peter Xu wrote:
> > > > Hi, Michael and the list,
> > > >
> > > > I observed this on windows 8 enterprise guests, when doing memory
> > > > ballooning:
> > > >
> > > > address@hidden:virtio_balloon_to_target balloon target: 0x80000000
> > > > num_pages: 524288
> > > > address@hidden:virtio_balloon_get_config num_pages: 524288 actual: 0
> > > > address@hidden:virtio_balloon_handle_output section name: pc.ram gpa:
> > > > 0x174604000
> > > > address@hidden:virtio_balloon_handle_output section name: pc.ram gpa:
> > > > 0x0
> > > > address@hidden:virtio_balloon_handle_output section name: pc.ram gpa:
> > > > 0x17460a000
> > > > address@hidden:virtio_balloon_handle_output section name: pc.ram gpa:
> > > > 0x0
> > > > address@hidden:virtio_balloon_handle_output section name: pc.ram gpa:
> > > > 0x17460b000
> > > > address@hidden:virtio_balloon_handle_output section name: pc.ram gpa:
> > > > 0x0
> > > > address@hidden:virtio_balloon_handle_output section name: pc.ram gpa:
> > > > 0x17460c000
> > > > address@hidden:virtio_balloon_handle_output section name: pc.ram gpa:
> > > > 0x0
> > > > address@hidden:virtio_balloon_handle_output section name: pc.ram gpa:
> > > > 0x17460d000
> > > > address@hidden:virtio_balloon_handle_output section name: pc.ram gpa:
> > > > 0x0
> > > > address@hidden:virtio_balloon_handle_output section name: pc.ram gpa:
> > > > 0x17460e000
> > > > address@hidden:virtio_balloon_handle_output section name: pc.ram gpa:
> > > > 0x0
> > > > address@hidden:virtio_balloon_handle_output section name: pc.ram gpa:
> > > > 0x17460f000
> > > > address@hidden:virtio_balloon_handle_output section name: pc.ram gpa:
> > > > 0x0
> > > > ...
> > > >
> > > > I think it's very possible that these zero addresses (please let me
> > > > know what the first 4K page is used for if anyone knows, since IIUC
> > > > that's what we throw away now) are half of the 64bit PFN. Or say, not
> > > > sure whether this means a windows guest driver bug that is using
> > > > 64bits for PFN rather than 32bits (and I suppose the protocol is using
> > > > 32bit for PFNs).
> > > >
> > > > Michael, do you know what to do with this?
> > > >
> > > > Thanks,
> > >
> > > PFN is GPA>>12. Do you have more than 1<<44 bytes of memory in this VM
> > > then?
> >
> > No. But isn't it still not good to drop the page at offset zero (and
> > drop it NNN times)?
>
> Absolutely - looks like a bug. I just don't know why does this happen.
IMHO if we are using a PFN array like this:
u64 pfn_array[];
In the windows guest driver, then we'll see this (as mentioned
above). But for sure this is wild guess of mine.
>
> > And I'm not sure what will happen if guest has
> > 1<<44 bytes; then we'll possibly drop very random addresses since a
> > real address will be splitted?
> >
> > Thanks,
>
> The balloon won't work, period. There was an interface change to fix
> that but implementation issues remained and contributor seems to be busy
> with page hints.
Okay. So IIUC this is already a known issue for the driver owner.
Then it seems that there's nothing more I can do for now...
Thanks,
--
Peter Xu